Networked solutions for industrial automation are known from the company magazine “Offene Kommunikation mit Standards” [Open Communication with Standards], W27-7481D, Moeller GmbH, November 2000 (Bonn). This printed publication already describes small control systems such as the control relay “easy”, which has a compact design and features an operator control unit, a display unit as well as an integrated computer unit. The printed publication also describes compact PLCs and modular PLCs (programmable logic controllers) that contain only the computer unit together with additional input/output units (I/O's) and are “operated” via separate input and visualization units, which are generally networked via bus systems. These input and visualization units are then formed, for example, by external personal computers or operator or touch panels.
These devices are intended for complex control tasks. In this context, it is a disadvantage that these devices either cannot, or only with corresponding effort, be mounted into the control panel of a control cabinet or the like at the site, that is, where the actual control unit is placed. In particular, sealing of the interior of the control cabinet can be accomplished only with considerable effort in the case of a touch panel that is installed in a control panel.
A standard way of mounting control and signaling devices in a control panel is exemplified in German Patent DE 44 46 167 C2. This document makes no reference to a modular combination of the control and signaling device with a further unit.
There are known ways of snap-in mounting of a housing in a bore of a panel (see German Utility Model Patent DE 82 32 239 U1). It is also known to design the operator control unit in such a manner that it is detachable from a control unit. German Patent DE 197 09 554 C1 proposes to design a device housing composed of upper and lower parts in such a manner that the upper and lower parts can be latched together. The upper part can optionally be composed of a control element or a fastening element. According to German Utility Model Patent DE 295 10 176 U1, it is known to secure an operator control module in keyhole-like openings in a mounting surface using pins. This simple mechanical attachment does not provide the electrical connection. The electrical connection must be accomplished separately, depending on the local conditions.
German Patent Application DE 198 25 584 A1 describes the mounting of a control and signaling device in a control panel. The control and signaling device has an opening in its rear fastening portion into which can protrude a further electrical unit. Means for direct coupling of the control and signaling device to the further electrical unit are not described in this document.